The invention relates to a scrubbing system for separating gaseous or particulate matter from gas streams, having a plurality of spin spray nozzles for injecting and distributing a wash liquid into the gas stream.
To separate gaseous or particulate matter from streams of air or gas, so-called "gas scrubbers" are used, in which a wash liquid is introduced from spray nozzles into the gas stream and distributed as uniformly as possible across its cross section. Such gas scrubbers, which are also called nozzle scrubbers, are used in large industrial models in flue gas cleaning apparatus in which acid flue gas components are removed, such as sulfur dioxide, chlorine or hydrogen fluoride, and to a lesser extent smoke particles, by the use of appropriate wash liquids.
The nozzles used in such gas scrubbers are made as a rule in the form of spin nozzles. The stream of liquid passing through the nozzle is subjected in the nozzle or upon leaving the nozzle to a spin, so that the liquid droplets plus the velocity components axially and radially--since the stream contains a conical spray--will also have a circumferential component. This spinning action has proven desirable for the spraying process, because it permits the achievement of a fine droplet spectrum, stability in the spray, and the fanning out of the spray to distribute the wash liquid in the gas stream. Spray nozzles of a similar kind, in which a spin is provided to produce a conical curtain, are disclosed in DE-OS 26 11 387, where a sprayer for sludge is described in which the liquid is introduced tangentially into a circular throat and exits at least across an edge in the form of a conical curtain of fine droplets.
It has been found that, in the arrangements mentioned above with a plurality of spin spray nozzles, disadvantages occur with regard to uniform sweeping through the scrubber, resulting in an impairment of performance. This is the case especially with gas scrubbers which, in the form of large flue gas scrubbers, operate on the countercurrent principle. In these the gas stream is introduced through a lateral gas injection connection into a guiding passage of the scrubber, flows through the latter from the bottom up, is sprayed in a countercurrent area with the washing fluid from a plurality of nozzles uniformly distributed on the cross section, and then exits again from a laterally or centrally disposed discharge. Between the injected wash liquid droplets and the gas flow an impulse exchange takes place which manifests itself mainly as a pressure loss which the flow undergoes in passing through the scrubber. But the spin produced in a uniform sense by the spray nozzles also brings the result that along the walls of the scrubber an impulse directed in and contrary to the direction of the entry of the gas stream is transferred to it, which again creates a large-area rotation of the field of flow of the gas stream. This in turn results in an asymmetrical flow through the gas scrubber. It has been found that the gas flow from the inlet can penetrate with little loss of pressure along the left wall of the scrubber to the left rear corner, and there it may be insufficiently cleaned and can rise with a relatively high velocity. The result is a very irregular and pronounced asymmetrical distribution of the residual contents in the gas flow behind the scrubber. Poor efficiency again results due to the irregular separation in the scrubber.
The present invention is therefore addressed to the problem of relieving the situation with simple measures.
For the solution of this problem, provision is made in a cleaning system of the kind described above so that spin spray nozzles with different spinning senses, with respect to the main direction of flow of the gas stream, to compensate for any spin in the main flow. By this configuration it is brought about that, due to the superimposition of the individual vortices of the spin spray nozzles arranged alternately with left-hand or right-hand spin, a cancellation of the spin components is produced, so that any reverse effect on the gas flow will not take place or will do so to only a greatly attenuated extent. This in turn leads to a uniform separation and thus to a higher efficiency, without the need for additional expensive measures.
In an advantageous embodiment of the invention, in a cleaning system with spin spray nozzles disposed side by side in rows, provision can be made for adjacent spin spray nozzles to have contrary spin senses in each row, so that, within a relatively small space, the desired superimposition of the individual vortices is achieved and with it a largely spin-free flow is achieved. It is advantageous in a further embodiment of the invention, in the case of a gas scrubber with a channel for guiding the gas stream, which has at a distance ahead of the spin spray nozzles an entrance for the gas stream entering into it, if the rows of spin spray nozzles run transversely of the direction of the entry of the gas stream into the guiding channel. In further embodiment of the invention, in the case of a gas scrubber with a guiding channel constructed symmetrically with a central plane running through the inlet, the spin nozzles which are on the left of the central plane have a spin contrary to the spin of the spin spray nozzles in a mirror image relationship with them on the right side of the central plane. It is, however, also possible to group nozzles of equal sense of spin to adapt them to the conditions of entry into the scrubber, so that the direction of flow can also be positively influenced thereby. Thus, in further embodiment of the invention, for example, the tangential component of the spin spray nozzles disposed adjacent to the walls of the guiding channel which run parallel to the central plane can be aimed at the side of the guiding channel which is provided with the inlet port. By such an arrangement of the nozzles an impulse component of the control field aimed against the inflow can be built up in the vicinity of the side walls of the scrubber. This works against the tendency of the gas flow to run along the shower-deprived side walls to the opposite scrubber wall and there to climb up contaminated. Instead, the still uncleaned flue gas is drawn more strongly into the intensive, neutral shower field of the scrubber.
In another embodiment of the invention, a spin spray nozzle, configured as a double spin spray nozzle with two coaxial spray jets discharging oppositely with opposite spin sense, is very especially suitable for a scrubbing system of the kind referred to in the beginning. Double-stream spin spray nozzles are known (DE 26 11 387 A1), but the two opposite sprays issue with the same spin. With such nozzles, therefore, compensating spin cannot be achieved in the flow.
Of course, it would also be possible, instead of the double spin spray nozzles with spray jets with opposite spin according to the invention, to provide two spin spray nozzles of a known kind, these nozzles being offset 180.degree. from one another. This, however, would necessitate the use of twice the number of spray nozzles, which would greatly increase the cost. The new double spin spray nozzles with their jets spinning in opposite senses are comparatively simple to manufacture, as will be explained further on. They require only one wash liquid connection if they are designed accordingly.
In another embodiment of the invention, the new spin spray nozzle therefore has two coaxially disposed spin chambers with their orifices aimed in opposite directions, which have a common inlet orifice in the area remote from the outlet openings which leads into each chamber with a branch which is aligned tangentially to the chamber wall which is associated but lies on opposite sides of the central plane of the inlet opening. With this configuration a common feed connection can be provided, yet due to the separate feed branches, different spin directions are achieved in the two oppositely issuing spray jets. Also the pulsation produced by the spray jets on the flow in the scrubber, which leads to a counter-pressure, is compensated by the new nozzle.
In another embodiment of the invention, both spin chambers can be parts of hollow cone or solid cone spray nozzles. The result is the possibility of configuring the nozzle as a hollow cone spray nozzle if a common dividing wall forms the bottoms of the spin chambers, and this dividing wall is provided with an opening in the axis of the nozzle. Carrying this idea further, the opening can be formed by a central constriction in the area of the feed opening of the spin chamber, and for further isolation of the spin chambers a hole disk whose diameter is not greater than one of the exit openings can be placed in the opening to permit installation of the hole disk.
The double spray nozzle, however, can also be configured such that the dividing wall is provided on both sides with elevations and depressions for the production of a solid cone spray jet. It is also possible, however, to dispense with a dividing wall, and in each spin chamber, which then does not have to have a branch running tangentially to its wall, to provide a spin insert which produces the desired contrary spin in the two spin chambers. Carrying this idea further, a dividing wall can be provided between the spin inserts and can have elevations to stabilize the flow.
Lastly, it is also possible to make the coaxial spin chambers and their discharge orifices of the same size, so that with such nozzles only a partial compensation of the spin is achieved, which can be advantageous when these nozzles are used in the wall area in the manner indicated previously.